Declining burden of malaria over two decades in a rural community of Muheza district, north-eastern Tanzania

Abstract

Background: The recently reported declining burden of malaria in some African countries has been attributed to scaling-up of different interventions although in some areas, these changes started before implementation of major interventions. This study assessed the long-term trends of malaria burden for 20 years (1992-2012) in Magoda and for 15 years in Mpapayu village of Muheza district, north-eastern Tanzania, in relation to different interventions as well as changing national malaria control policies.

Methods: Repeated cross-sectional surveys recruited individuals aged 0 - 19 years from the two villages whereby blood smears were collected for detection of malaria parasites by microscopy. Prevalence of Plasmodium falciparum infections and other indices of malaria burden (prevalence of anaemia, splenomegaly and gametocytes) were compared across the years and between the study villages. Major interventions deployed including a mobile clinic, bed nets and other research activities, and changes in national malaria control policies were also marked.

Results: In Magoda, the prevalence of P. falciparum infections initially decreased between 1992 and 1996 (from 83.5 to 62.0%), stabilized between 1996 and 1997, and further declined to 34.4% in 2004. A temporary increase between 2004 and 2008 was followed by a progressive decline to 7.2% in 2012, which is more than 10-fold decrease since 1992. In Mpapayu (from 1998), the highest prevalence was 81.5% in 1999 and it decreased to 25% in 2004. After a slight increase in 2008, a steady decline followed, reaching <5% from 2011 onwards. Bed net usage was high in both villages from 1999 to 2004 (≥88%) but it decreased between 2008 and 2012 (range, 28% - 68%). After adjusting for the effects of bed nets, age, fever and year of study, the risk of P. falciparum infections decreased significantly by ≥97% in both villages between 1999 and 2012 (p < 0.001). The prevalence of splenomegaly (>40% to <1%) and gametocytes (23% to <1%) also decreased in both villages.

Discussion and conclusions: A remarkable decline in the burden of malaria occurred between 1992 and 2012 and the initial decline (1992 - 2004) was most likely due to deployment of interventions, such as bed nets, and better services through research activities. Apart from changes of drug policies, the steady decline observed from 2008 occurred when bed net coverage was low suggesting that other factors contributed to the most recent pattern. These results suggest that continued monitoring is required to determine causes of the changing malaria epidemiology and also to monitor the progress towards maintaining low malaria transmission and reaching related millennium development goals.

Figure 1

Overall prevalence of Plasmodium falciparum infections and interventions deployed in Magoda and Mpapayu villages in Muheza district from 1992 to 2012.

Figure 2

Age-specific prevalence of Plasmodium falciparum infections in the villages of Magoda (A) and Mpapayu (B) between 1999 and 2012. Confidence intervals were calculated by Wilson score method.

Figure 3

Age-specific geometric mean of Plasmodium falciparum density (asexual parasites/μl) in the villages of Magoda (A) and Mpapayu (B) between 1999 and 2012. Data of under-fives from Mpapayu village (B) in 2010 and 2011 were excluded from the analysis because individuals seen were few and had high parasite density (4 with geometric mean parasite density of 21,744 and one participant with 31,200 asexual parasites/μl, respectively). In Mpapayu, no study participant aged <5 years old had malaria parasites in 2012.

Figure 4

Proportion of under-fives and study participants aged ≥5 years who reported to have slept under bed nets in the past 24 hours before the survey in the villages of Magoda (A) and Mpapayu (B) in Muheza district between 1999 and 2012.